The Composition, Isotopic Characteristics And Sources Of Organic Matter In The Yellow River Suspended Particulates And Adjacent Bohai And Yellow Sea Surface Sediments

Marginal seas could account for up to80%of the marine sediment organic burial, thusthey play a significant role in the global and regional organic carbon cycle. However, thepotential importance of marginal sea system in global and regional organic carbon budgets isstill unclear. One reason is the inherent complexity and variability of rivers, in which fluvialorganic matters (OM) exhibit tremendous temporal and spatial variation in physical andchemical characteristics. Another reason is how to trace of various sedimentary organicmatters which initial composition and isotopic characteristics may have potential to varyduring delivery to, subsequent deposition and re-deposition over the seafloor. This variabilitymakes it difficult to constrain carbon budgets by simply measuring bulk parameters such asTOC/TN, δ13Cbulkand Δ14Cbulk. In order to develop a more complete view of the composition,sources and ages of organic matter delivery in the climatically sensitive Chinese region. Inaddition to bulk properties, I measured the abundance and isotopic composition (Δ14C、δ13Cand δD) of source-specific biomarkers from12near-surface suspended particulate mattersamples collected nearby Kenli,~50km upstream of the river mouth, as part of a samplingcampaign between June2011and July2013and8surface sediments in the adjacentBohai&Yellow Sea. The overall goals of this thesis are therefore a) to discuss temporal andspatial variations in the isotopic compositions of various biomarkers and their controllingeffects, b)to first develop content and compound-specific13C and14C measurements ofsource-specific biomarkers to quantify OM sources in the Yellow River suspendedparticulates and the Bohai&Yellow Sea, c)to develop an initial framework in which the14Cage of sedimentary OM in marginal sea can be more quantitatively expressed in terms of acontemporary marine component, a pre-aged terrestrial constituent and a truly ancientcomponent, and d)to evaluate preliminarily the transport histories of terrigenous OMincluding latter transportation and degradation. POC in the Yellow River exhibits relatively uniform13C values, and old radiocarbonages (4000to4690yr), illustrating a highly refractory and detritus feature consisting of highlydecomposed organic matter. And the contribution of recent biosynthesized OM is supposed tooccupy only small fraction of POC in the Yellow River. Radiocarbon ages of short-chain fattyacids were variable but generally modern (650yr to great than modern), suggesting they aresourced from both fresh terrestrial debris, but more likely from aquatic productivity duringlow-turbidity periods. Lignin phenols displayed a significant temporal variability and relativeyounger in radiocarbon age (1780yr to great than modern), most likely reflecting thecontribution of fresh woody debris eroded from coarse soil particles in organic and surfacesoil layers. In contrast, long-chain fatty acids (n-C26,28,30) and Alkanols (n-C24,26,28)displayed a relatively narrow and pre-aged range in radiocarbon age (1450to2180yr and1180to2170yr, respectively), reflecting contribution of pre-aged, soil-derived OM without astrong seasonal plant debris14C signal such as lignin phenols. Compared with the abovebiomarkers, old radiocarbon ages (2670to7550yr) were observed on long chain n-alkanes(n-C29,31). Furthermore, weighted average δ13C and Δ14C of n-C29,31alkanes significantlylinear correlated with the CPIΣ25~33alkanevalues, pointing to at least two sources: pre-aged soiland a ancient component likely derived from erosion of ancient sedimentary rocks uplifted inthe upstream and numerous coal mines distributing broad along the middle reach of the river.On the molecular14C level, fluvial OM components showed contrasting14Ccharacteristics. POC in the Yellow River can be regarded as three constitutes including binarymodern source from plant debris and aquatic production (Δ14CM=0‰54‰, modern)deduced by short chain fatty acids, pre-aged mineral-bound soil OM (Δ14CS=-208‰23‰，1810±230yr) addressed by long chain fatty acids and ancient source deduced by long chaineven alkanes (Δ14CP=-1000‰，>20000yr). A coupled molecular isotopic mass balance modelbased on compound-specific biomarkers δ13C andΔ14C assessed, on average, roughly18%±11%of the recent biosynthesized or microbial reworking labile OM,50%±13%ofpre-aged soil OM and32%±3%of ancient OC likely derived from the physical weathering ofancient rock.δ13C andΔ14C of POC in the Bohai&Yellow Sea surface sediment exhibited to slightly more enriched values with distance offshore, consistent with an increasing contribution frommarine production. Short chain fatty acids showed enriched in13C (-25.1‰~-27.4‰) andcontemporary radiocarbon ages, reflecting a strong marine algal/bacteria contribution with amodern radiocarbon ages. Allochthonous sediments lateral transport process and sedimentenvironment stability appeared to control the spatial distribution of14C isotopic compositionof short chain fatty acids. Extremely depletedΔ14C of short chain alkanes (n-C16,18)suggested a predominant input from ancient sources to n-C16、18alkanes. The radiocarbon agesof three terrestrial lipid biomarkers (3800±1730yr for n-C26,28,30fatty acids,4860±1750yr forn-C27,29,31alkanes,2940±1700yr for n-C24,26,28Alkanols) displayed a similar spatialdistribution pattern and generally older than that of corresponding biomarkers in the YellowRiver particulates, illustrating part of pre-aged terrestrial OM from the river to the marinesedimentary OM was remineralized. Based on the molecular distributions and δ13C isotopiccharacteristics, sedimentary n-C26,28,30fatty acids and n-C24,26,28Alkanols appeared clearlyinfluence by marine sources, especially at the site located in the center of the southern YellowSea. However, n-C27,29,31alkanes exhibited similar depleted δ13C (-29.9‰~-31.2‰) value inall sites, suggesting a predominant input from terrestrial sources instead of modern marinebiota. Thus, n-C27,29,31alkanes likely provide better estimates of pre-aged terrestrial OM.A coupled molecular isotopic mass balance model based on compound-specificbiomarkers δ13C and Δ14C assessed, on average, roughly41%~70%of marine OM,12%~50%of pre-aged terrestrial OM and0%~34%of ancient OC likely derived from the physicalweathering of ancient sedimentary rock. This source assessment shows the highestcontribution of marine OM, pre-aged terrestrial OM and ancient OM appears respectively atthe center of the South Yellow Sea (maximum70%), modern/old Yellow River delta(maximum50%) and north area of old Yellow River mouth (maximum34%).In conclusion, above source assessments implies that~80%of particulate OM deliveredfrom the Yellow River to the marine sediment is refractory and altered plant derived pre-agedsoil OM and ancient ancient OM (>1800yr). Results also indicate that roughly30~49%of theOM currently being buried in the Bohai&Yellow Sea is derived from the pre-aged soil andthe weathering of ancient sedimentary rock. The two old terrigenous organic carbon contribution only effect on biologically mediated carbon cycles of the continental and marineenvironments over long term geologic time scales (several thousands or millions of years),without influence on contemporary/modern carbon cycle (<100yr time scale).